The present invention relates to a method of operating a water-turbine or a pump water-turbine and, more particularly, to a method of operating a water-turbine or a pump water-turbine having an improved controlling operation of the main turbine tripping circuit, which acts upon detection of a shortage of cooling water in the runner seal portion, which is liable to take place during no-load operation such as in the case of phase adjusting running of the water-turbine or pump water-turbine.
In general, in the operation of the hydraulic machine such as water-turbine, pump water-turbine or the like directly connected to an alternator, the water level in the runner chamber is lowered to make the runner idle to create a state called "phase modification running", in order to increase the power factor of the power line, when the power factor is lowered. It is also a common measure to conduct a so-called stand-by running of the water-turbine or the pump water-turbine to make the latter ready for the loaded running. The stand-by running is made in a manner similar to the phase modification running. There are various ways of starting of the phase modification running. According to a first method, the water level in the runner chamber is lowered while stopping the main machine consisting of the alternator and the water-turbine or the pump water-turbine, and the phase modification running is commenced after accelerating the water-turbine to the rated speed by means of a starting motor. This method is substantially the same as the ordinary pump starting method.
According to a second method, the water inlet valve is opened to fill the casing and then the guide vanes are opened to a predetermined opening degree to start the runner. The alternator is then put into the power line after the speed is increased to the rated speed. Thereafter, the guide vanes are fully closed and the water level in the runner chamber is depressed by compressed air to make the runner idle, thereby to create the state of the phase modification running.
In the first method stated above, it is rather easy to lower the water level because the main machine is not rotating. This method, however, requires a provision of a starting motor, and takes a considerably long time for starting and accelerating the main machine to the rated speed. For this reason, the second method is generally preferred to the first method.
The gaps of the runner seals between the rotating runner and the stationary parts of the upper and lower covers are small. Therefore, when the runner idles with the lowered water level in the runner chamber for the phase modification, the temperature of the runner is inconveniently raised due to the torque resistance imposed by the water from the casing side through the guide vanes. In consequence, the runner is thermally expanded to make contact with the stationary parts dangerously.
To avoid this danger, means are provided for supplying the runner seals during idling of the runner to prevent the breakdown of the runner due to contact with the stationary parts of the runner seals.
In general, the pressurized water still remains in the runner seals in the period immediately after the depression of the water level because, in such a period, the inlet valve has not been closed completely yet. It is, therefore, not necessary to supply the cooling water to the runner seals in such a period.
The conventional operation system includes a function to actuate a main machine tripping circuit upon detect of the shortage of the cooling water supplied to the runner seals. It is often experienced that the tripping circuit is undesirably activated upon detection of the shortage of the cooling water even in the above mentioned period in which the supply of cooling water is unnecessary, so that the main machine is tripped unnecessarily.